1. Technical Field
The present invention relates to an apparatus for damping oscillatory movement between parts, and particularly relates to a vehicle engine mount for damping engine vibrations.
2. Background Art
Devices for damping oscillatory movement between parts are well known. Certain of such devices include a field responsive fluid such as an electrorheological fluid, a ferro fluid or a magnetic fluid. The apparent viscosity of the fluid in such devices varies as a function of the magnitude of an energy field applied to the fluid. By controlling the apparent viscosity of the fluid, the damping characteristics of the device can be controlled.
A spring having a field responsive fluid and means for applying an energy field to the fluid is disclosed in U.S. Pat. No. 4,869,476, issued on Sep. 26, 1989 and assigned to the assignee of the present invention. By varying the energy field applied to the fluid, spring characteristics such as spring rate and load-carrying capacity can be varied. The spring is connectable between relatively movable parts to resist movement between the parts and to urge the parts to an initial position when the parts are moved therefrom.
A known damping device using magnetic fluid to control operating characteristics of the device is disclosed in U.S. Pat. No. 3,059,915. The device of U.S. Pat. No. 3,059,915 controls flow of a magnetic fluid through a passage. The rate of fluid flow through the fluid passage varies as a function of the magnitude of a magnetic field applied to the fluid in the fluid passage. The damping characteristics of the device depend upon the rage of fluid flow through the fluid passage.